A proximity sensor detects the presence of a nearby person or object in a region or area. A proximity sensor may employ an electromagnetic or electrostatic field, or a beam of electromagnetic radiation, e.g., infrared, or acoustic energy and detect changes in the field or return signal. Proximity sensing can utilize different sensor types for different types of target objects. For example a photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor might be used to detect a metal target.
Different types of proximity sensors have different maximum distances within which the sensors can detect an object. Some sensors have adjustments of the nominal distance range or means to report a graduated detection distance. Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between sensor and the sensed object.